Methods for Transferring Colored Markings Onto Plastic Surfaces

Abstract

The invention relates to a method for transferring colored markings or labels onto plastic surfaces by means of a laser beam, to a transfer medium for carrying out said method and to articles, the plastic surfaces of which are laser-marked or laser-labeled by way of such a method.

Claims

1. Method for transferring colored markings or labels onto plastic surfaces by means of a laser beam, wherein a multilayer planar transfer medium, having at least one carrier layer (1) containing at least one material which absorbs energy emitted by the laser beam, one metal layer (2) consisting of a sublimable metal and arranged directly on the carrier layer (1), and a labeling medium (3*) arranged directly on a side of the metal layer (2) facing away from the carrier layer (1) and containing at least one color component, is contacted from the side of the carrier layer (1) on a defined surface unit with a pulsed laser beam, wherein the metal of the metal layer completely sublimates in a locally selective manner and the labeling medium (3*) is simultaneously detached from the carrier layer in a locally selective manner, and wherein the labeling medium detached from the carrier layer is transferred to the plastic surface in an adherent manner.

2. Method according to claim 1, characterized in that the carrier layer is a single- or multilayer polymer film, wherein at least one of the layers of the polymer film contains a material which absorbs energy emitted by the laser beam.

3. Method according to claim 1 of 2, characterized in that the material which absorbs energy emitted by the laser beam is carbon, carbon black, anthracene, perylenes, rylenes, pentaerythritol, copper hydroxide phosphates, molybdenum disulfide, antimony (III) oxide, iron oxides, bismuth oxychloride, or coated or uncoated plate-like sheet silicates or graphite platelets.

4. Method according to one or more of claims 1 to 3, characterized in that the metal layer is a layer made of aluminum, magnesium, copper, tungsten, tin, zinc, silver or gold, having a layer thickness in the range from 1 to <10,000 nm.

5. Method according to claim 4, characterized in that the metal layer has a layer thickness in the range from 3 to 50 nm.

6. Method according to one or more of claims 1 to 5, characterized in that the labeling medium (3*) has a multilayer structure and at least one layer that contains the color component (3) and at least one further layer that represents a sealing layer (3″) and/or an adhesive layer (3′).

7. Method according to one or more of claims 1 to 6, characterized in that a laser is used to generate the pulsed laser beam, the frequency-dependent pulse energy of which generates an energy input into the metal layer that is greater than the specific enthalpy of sublimation ΔH.sub.sub of the metal of the metal layer.

8. Method according to claim 7, characterized in that the laser is a pulsed solid-state laser or a pulsed fiber laser with emission wavelengths of 534 nm or 1064/1062 nm.

9. Method according to one or more of claims 1 to 8, characterized in that the at least one color component in the labeling medium (3*) is selected from the group consisting of organic and inorganic colorants.

10. Method according to claim 9, characterized in that the organic colorants are azo pigments, azo dyes, perinones, perylenes, anthraquinones, flavanthrones, isoindolinones, pyranthrones, anthrapyrimidines, quinacridones, thioindigo, dioxazines, indanthrones, diketopyrrolopyrroles, quinophthalones, phthalocyanines, azo complexes, azomethine complexes, dioxime complexes, isoindolinone complexes, and/or carbon black.

11. Method according to claim 9, characterized in that the inorganic colorants are metal pigments, oxide pigments, oxide hydroxide pigments, oxide mixed-phase pigments, metal salt pigments, sulfide or sulfide selenium pigments, complex salt pigments, silicate pigments and/or plate-like effect pigments.

12. Method according to one or more of claims 1 to 11, characterized in that it is carried out at a write speed in the range from 500 to 60,000 mm/s.

13. Transfer medium for the adherent transfer of colored markings or labels onto plastic surfaces by means of a laser beam, which has a multilayer structure and at least one carrier layer (1) containing at least one material which absorbs energy emitted by the laser beam, one metal layer (2) consisting of a sublimable metal and arranged directly on the carrier layer (1), and a labeling medium (3*) arranged directly on a side of the metal layer (2) facing away from the carrier layer (1) and containing at least one color component.

14. Transfer medium according to claim 13, characterized in that the metal layer is a layer made of aluminum, magnesium, copper, tungsten, tin, zinc, silver or gold, having a layer thickness in the range from 1 to <10,000 nm.

15. Transfer medium according to claim 13 or 14, characterized in that the labeling medium (3*) has a multilayer structure and at least one layer that contains the color component (3) and at least one further layer that represents a sealing layer (3′) and/or an adhesive layer (3″).

16. Transfer medium according to one or more of claims 13 to 15, characterized in that the at least one color component in the labeling medium (3*) is selected from the group consisting of organic and inorganic colorants.

17. Article containing a plastic surface which is laser-marked or laser-labeled using a method according to one or more of claims 1 to 12.

18. Article according to claim 17, characterized in that it is an article made of plastic or an article having at least one surface made of plastic.

Description

DESCRIPTION OF THE FIGURES

[0085] FIG. 1: shows the basic layer structure of a transfer medium according to the invention with a three-layer labeling medium containing color layer (3), adhesive layer (3″) and sealing layer (3′)

[0086] FIG. 2: schematically shows the laser process with the transfer medium applied to the plastic surface and the effect of the laser radiation on the rear side of the carrier layer (1)

[0087] FIG. 3: shows the schematic representation of a lasered barcode (example code 128) on a plastic surface, produced by the laser method according to the invention

[0088] FIG. 4: shows colored (left side; from top to bottom: green, red, yellow), right side (left: blue) and achromatic (right side, right: white on black, black on white) labels on black/white PP plastic surfaces, produced with the method according to the invention

[0089] FIG. 5: shows a gold-colored label on a black PP plastic surface (left) with the effect pigment Iriodin® Solar Gold (Merck KGaA) and the associated labeling medium after the laser process (right)

[0090] The present invention provides a method for transferring colored markings or labels of plastic surfaces by means of a laser beam, which can produce colored markings/labels with great line definition, in clear colors and effect colors at high operating speeds of the laser. Since a close contact between the plastic surface and the transfer medium by mechanical pressure or vacuum is not required, three-dimensional articles with an unusually shaped surface and/or greater surface roughness can also be labeled without any problems. The method according to the invention therefore represents a valuable addition to and improvement of methods for laser transfer of colored markings that are already available on the market. A transfer medium that can be used for the method according to the invention and the products produced by means of the method according to the invention offer corresponding advantages.

[0091] The present invention will now be described by means of examples of the invention but is not restricted to these examples.

EMBODIMENTS

[0092] For all examples, carrier films are used which are PET films (1) colored black with carbon black as a laser absorber and vaporized with a thin aluminum layer (2).

[0093] Depending on the layer thickness, the individual layers of the labeling medium are applied to the carrier film using commercially available printing processes such as flexo, gravure, or screen printing or knife-coating. Depending on the type of printing inks used, i.e., water-based, solvent-based or UV inks, the layers are dried or cured with UV light.

Example 1: Producing a Sealing Layer (3′)

[0094] The sealing layer guarantees reliable protection of the color layer against external influences in the end application.

[0095] Variant 1: At first, a solvent mixture is prepared from 40 wt. % of methyl ethyl ketone, 23 wt. % of toluene and 10 wt. % of cyclohexanone, in which 19.5 wt. % of PMMA powder from Degussa (T.sub.g: 122° C.) and 7.5 wt. % of PE wax are dissolved, and the mixture is homogenized. The mixture is applied to the aluminum-vaporized side of the black carrier film with a 60 screen dots/cm gravure printing cylinder.

[0096] Variant 2: At first, 57 wt. % of xylene is provided and 28.6 wt. % of polystyrene and 14.4 wt. % of PE wax are dissolved therein, the mixture is homogenized and then applied to the aluminum-vaporized side of the black carrier film with a 60 screen dots/cm gravure printing cylinder.

Example 2: Producing a Blue Color Layer (3)

[0097] Producing a blue printing ink is described as an example of any color layer, without being limited to blue. In FIG. 4, differently colored embodiments (green, red, yellow) are shown.

2.1

[0098] For gravure printing: A blue solvent-based gravure printing ink is produced by mixing 30 wt. % of process blue or 30 wt. % of Pantone blue with 70 wt. % of a nitrocellulose lacquer from Siegwerk, adjusted to the appropriate viscosity with ethanol/ethyl acetate and printed with a 60 screen dots/cm gravure printing cylinder on the aluminum-vaporized side of the black carrier film or on a sealing layer.

2.2

[0099] For screen printing: A blue water-based screen printing ink is produced by mixing 15 wt. % of Aqua Jet navy blue 522 in Aqua Jet FGLM 093 from Pröll and optionally 1.5 wt. % of L36459 defoamer from Pröll, adjusted to the appropriate viscosity with water and printed with a 61-64 or 77-55 screen on the aluminum-vaporized side of the black carrier film or on a sealing layer.

Example 3: Producing a Color Layer with Effect Pigments (3)

[0100] A solvent-based gravure printing ink is produced by mixing 30 wt. % of Iriodin® 305 (Iriodin® Solar Gold) from Merck KGaA with 70 wt. % of a nitrocellulose lacquer from Siegwerk, adjusted to the appropriate viscosity with ethanol/ethyl acetate and printed with a 60 screen dots/cm gravure printing cylinder on the aluminum-vaporized side of the black carrier film or on the sealing layer (for results after carrying out the method according to the invention, see FIG. 5).

Example 4: Producing an Adhesive Layer (3″)

[0101] The adhesive layer (3″) is optionally applied to the color layer (3) in order to strengthen the adhesion of the labeling medium to the plastic surface. For this purpose, polymer-containing films known to a person skilled in the art are used, which soften under the action of heat from the laser radiation and bond with the plastic surface.

[0102] For example, a solvent mixture of acetone and toluene at a ratio of 1:3 is prepared, in which 5 wt. % of PVC powder is dissolved, and the mixture is homogenized. The mixture is then applied to the color layer (3) with a 60 screen dots/cm gravure printing cylinder.

[0103] The layer thicknesses of the individual layers in the transfer media of the examples are in each case set in the ranges 10-75 μm for the black carrier film, 40-45 nm for the aluminum layer, 4-9 μm for the sealing layer, 2-12 μm for the color layer, and 0.3 to 2 μm for the adhesive layer of the labeling medium.

[0104] For carrying out the method according to the invention, the labeling media are applied to the plastic surface to be labeled and labeled in color with an Nd:yttrium vanadate solid-state laser or a fiber laser (FIG. 2, 3, 4). In order to determine the suitable laser parameters, a test grid is used in each case, which covers the following performance/parameter windows in pulse mode:

1. Nd:YVO.sub.4 laser from Trumpf (type VMc 5): [0105] a. Wavelength: 1,064 nm [0106] b. Output power: 10 W [0107] c. Peak pulse power: 10-40 kW (depending on frequency) [0108] d. Performance in the test grid: 10-100% (based on an output power of 10 W) [0109] e. Frequency in the test grid: 20-100 kHz [0110] f. Speed in the test grid: 500-5,000 mm/s
2. Fiber laser from KBA-Metronic (type F-9050, UHS) [0111] a. Wavelength: 1,062 nm [0112] b. Output power: 50 W [0113] c. Peak pulse power: 20 kW (depending on frequency) [0114] d. Performance in the test grid: 30-100% (based on the output power of 50 W) [0115] e. Frequency in the test grid: 20-100 kHz [0116] f. Speed in the test grid: 4,000-60,000 m m/s

[0117] In this case, the distance between the labeling medium and the plastic surface can be up to 100 μm, preferably up to 75 μm.

[0118] It can be stated that colored plastic labels with very high marking speeds of up to 60,000 mm/s (fiber laser) can best be realized using a thinner color layer, e.g., produced with gravure printing.

[0119] Very good colored labels can be achieved, e.g., with the following laser parameters (Table 2), without being limited to these laser parameters.

TABLE-US-00002 TABLE 2 Laser parameter ranges for plastic labels Power [%] (based on the respective laser output Frequency Laser type Color layer power) [kHz] Speed [mm/s] Nd:YVO.sub.4 Example 2 with 60-99 20-90 2,500-4,000 screen printing Example 2 with 70-90 40-80 2,500-5,000 gravure printing Fiber laser Example 2 with  60-100 30-70  4,000-60,000 screen printing Example 2 with 20-40  40-100 20,000-60,000 gravure printing

[0120] The plastic labels shown in FIGS. 4 and 5 are achieved with the following laser parameters (Table 3):

TABLE-US-00003 TABLE 3 Laser parameters for colored and achromatic plastic labels and plastic labels with effect pigments (for PP, FIGS. 4 and 5) Power [%] (based on the respective laser output Frequency Speed Laser type Plastic label power) [kHz] [mm/s] Fiber green on black PP 85 40 50,000 laser red on black PP 85 25 30,000 yellow on black PP 75 25 40,000 green on white PP 85 40 50,000 red on white PP 85 40 20,000 yellow on white PP 65 20 45,000 blue on black PP 85 45 30,000 Nd:YVO.sub.4 blue on white PP 70/65 50 1,000 blue on transparent TPU 75-95 10 500-750 Fiber white on black PP 75 15 50,000 laser black on white PP 90 30 30,000 Iriodin ® Solar Gold on 40-60 30-60 60,000 black PP